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Different switches explained

Railwayscenics list various different types of switches and it is easy to be confused by the sheer variety. This page tries to explain the different types and terminology used.

Technical Definations:

Pole - number of switch contact sets.Throw - number of conducting positions, single or double.Way - number of conducting positions, three or more.Momentary (non-latching) - switch returns to its normal position when released.Open - off position, contacts not conducting.Closed - on position, contacts conducting, there may be several on positions.

Switch Contact Ratings

All switch contacts are rated with a maximum voltage and current and we list these where possible. There may be different ratings for AC and DC.

For low voltage electronics projects the voltage rating will not matter, but you may need to check the current rating. The maximum current is less for inductive loads (coils and motors) because they cause more sparking at the contacts when switched off.

Never exceed any of the given ratings as this may cause premature failure of the switch.

Types of switches

Slide Switch: With Slide Switches the switching movement is in a linear to and fro motion. They cost little, the range is limited and they mount discreetly.

Toggle Switch: Toggle Switches have a to and fro switching movement but through an arc. They cost more than sliders but the bigger range will cover almost any switching situation. They are easy to install and look good on a track diagram or switchboard. Toggle switches are the most familiar switches. The simple toggle switch is available in various configurations depending on the number of poles and switching positions.

Rocker switch: A rocker switch has a seesaw action. You press one side of the switch down to close the contacts, and press the other side down to open the contacts.

Rotary Switch: As the name denotes, rotary switches are activated by rotating a knob. They are generally needed when the number of circuits that need to be changed simultaneously exceeds the capacity of a toggle or slide switch. Rotary (Multi-way) Switches have many conducting positions. They may have several poles (contact sets). They are available with a range of contact arrangements from 1-pole 12-way to 4-pole 3-way.For different variants of the rotary switch, the number of ways (switch positions) are reduced with a different stop under the fixing nut, limiting the movement where there are more poles to be served.

Micro switch: A micro switch is an electrical switch which can be operated using a very small force and also possibly using a small movement. Generally have external lever arms that operate switch.

Push button switch: A pushbutton switch is a switch that has a knob that you push to open or close the contacts. In some pushbutton switches, you push the switch once to open the contacts and then push again to close the contacts. In other words, each time you push the switch, the contacts alternate between opened and closed. These types are commonly called latching switches. There are also Non latching push button switches that only maintain the switch contacts when the switch is help in position. Once the switch is let go, the current is broken and the switch turns off. Push switches are usually a simple on-off switch.

Reed switch: Magnetic Reed Switches are long thin wire-like switches that are activated by the presence of a magnet. You can place one of these under the track rails between the ties and place a small magnet on the bottom of a railcar, so that when the railcar with the magnet travels over the switch, the device that the switch is connected to will be activated (e.g, a light in a building, a section of track or an animated device).Normally open - In a reed switch, the two contacts (which look like metal reeds) are made from magnetic material and housed inside a thin glass envelope. (You can see this quite clearly in our top photo.) As you bring a magnet up to a reed switch, it magnetizes the contacts in opposite ways so they attract and spring together and a current flows through them. A reed switch like this is normally open (NO) (normally off), unless a magnet is positioned right next to it, when it switches on.Normally closed - You can also get reed switches that work the opposite way. The two contacts are normally snapped together. When you bring a magnet up to the switch, the contacts magnetize, repel one another, and split apart, opening the switch and breaking the circuit. Reed switches like this are called normally closed (NC) (normally switched on), and they switch off when you bring a magnet up to them.

Switch poles and throws explained

SPST or Single Pole Single Throw The single throw electrical switch is an On-Off type switch. One flip of the switch turns the light on, Flip the switch the other way and it turns off. Used mainly to interrupt current for a single pole of a circuit.

DPST or Double Pole Single Throw A double throw switch is an either-or type switch. You have either one light on or another but not both. Or you have either one section of track powered on or another but not both at the same time. In other words, if you flip the switch one way, Light A comes on and Light B goes off. Flip it the other way, Light B comes on and A goes off. This switch could isolate both live and neutral poles or one could use it for switching two different circuits simultaneously.

SPDT or Single Pole, Double Throw (ON-ON) This switch can be on in both positions, switching on a separate device in each case. It is often called a changeover switch. For example, a SPDT switch can be used to switch on a red lamp in one position and a green lamp in the other position.A SPDT toggle switch may be used as a simple on-off switch.

SPDT Centre Off - ON-OFF-ON A special version of the standard SPDT switch. It has a third switching position in the centre which is off. Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released.

DPDT or Double Pole Double Throw Centre-Off These can be very useful for motor control because you have forward, off and reverse positions. Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released.

Fitting switches

Most switches will have a threaded segment below the lever which allows the switch to be secured into a panel using a lock nut and nut. They are fitted from the rear, into a hole drilled the size of the switch mount. A nut is used to secure the switch from the front. As well as 2 nuts a serrated washer and a special washer that can lock the switch into a notch filed in the hole are provided to prevent the switch spinning round in the hole.

Rocker switches, that we do not sell, generally require a rectangular cut out, and are then push through the hole from the front and secured using a sprung tab.

Reed switches are fitted by drilling a small hole the sixe of the wire leads, and bending these to fit the location.

Connecting and wiring switches

Most of the switches that we sell come with tinned solder tag connections and this makes soldering wires to the terminals easy as long as the switch does not get too hot in the soldering process.

Some of the switches come with tab connections and it is possible to use our crimp on connectors to wire these types. The connectors and terminals come in different sizes so be sure to read the product specifications before buying the connectors.

How ever you wire the switches, please ensure that any bare wires or connections are insulated with either tape or heat shrink just for safety.